How To Unclog Clogged Drains

Drains are pretty simple and diagnosing a problem is simple if you understand the drain, waste and vent (DWV) system. To diagnose the problem, understand the DWV system and then follow this explainer to narrow down the problem, and solution.

Water flows down hill. The whole DWV system is built on this principle. Most drain systems are gravity flow systems. Each drain in your home travels
down to a larger branch drain. All the branch drains connect
to the main drain or sewer line. A large pipe leaves your home
and leads to the city sewer or your own septic system. All of
this is downhill, all the way to the sewer or septic. In some
cases, a home's sewer line will be below the level of the city sewer, or a basement bathroom is below the home's main sewer line and so pump equipment must be used to move the waste out to the main sewer or septic.

Along with all the drain and waste pipes, there are some vent pipes integrated
into the system. These vent pipes allow sewer gas to be vented out above your home where it can quickly mix with the air and dissipate. The vents also serve the important function of preventing a vacuum or siphon from occurring. If a vacuum occurs, the draining water slows down and then becomes more prone to clogging. A siphon can also pull the water in the drain traps, which will then allow sewer gas to enter your home.

Problem

Solution

I smell a bad odor near a sink, shower, tub or toilet

Check vents for blockages.

Unused sinks, etc. may allow the water in the trap to evaporate - add water.

Add bleach to the drain to kill bacteria.

Clear partial clog that is harboring bacteria.

Toilet may have gaps between it and the wax ring, replace the wax ring.

Vent line may have deteriorated or separated allowing sewer gas to vent into your home.

Only one toilet or sink or shower or tub or appliance is backing up

When just one fixture is backing up, it is probably a clog close to that fixture. Use basic drain clearing steps to clear the drain.

More than one toilet or sink or shower or tub or appliance are backing up, in the same part of the home, but the rest of the drains in the home are working properly

A branch drain or vent line is clogged and needs to be cleared, probably with a drain snake or pressure device. Chemicals are not very effective on this type of clog.

More than one toilet or sink or shower or tub or appliance are backing up, in different parts of the home

Assuming it is not coincidental and two separate local clogs are causing the problem, it is likely the main sewer drain from your home is blocked. It may be a clog that can be cleared with a drain snake or pressure device.

In the case of tree roots or a damaged sewer pipe, more serious intervention may be required. Consider hiring a pro.

If you have a septic system, it may be full and needs to be pumped out.

Sewage is backing up into your home, way beyond just an overflowing toilet

The city sewer probably has a major blockage and you are downhill from other people's homes. Their sewage is backing up through your main sewer drain. Contact the city.